Image forming apparatus and image forming method

ABSTRACT

A downtime relating to formation and detection of a detection image is reduced. An image forming apparatus includes a controller configured to calculate a first conversion unit to convert a gradation of input image data so that density output for the input image data becomes a first density output characteristic based on a first detection result of the detection image detected by a density sensor in a first mode. The controller generates a second conversion unit to convert the gradation of the input image data so that the density output for the input image data becomes a second density output characteristic in the second mode based on the detection result in the first mode and correction information, and further updates the correction information based on a second detection result of the detection image detected by the density sensor in the second mode and the first detection result.

BACKGROUND Field of the Disclosure

The present disclosure relates to an image forming apparatus and animage forming method, and more particularly, to an image formingapparatus having a variable density image formation mode of controllinga supply amount of developer to be supplied to an image bearing memberby a developer supply member.

Description of the Related Art

In a field of image forming apparatus, there is used a γ curve obtainedby expressing a correlation between an input image signal and a densityof an output image corresponding to the input image signal as a curvedline. There is also known a so-called look-up table configured toconvert a gradation of the input image signal so as to obtain lineardensity characteristics of the output image with respect to the inputimage signal. Correction using this look-up table is referred to asso-called “γ correction”. In addition, there is known a method in which,when the γ curve collapses due to, for example, an operating environmentand a continuous operation time of the image forming apparatus, theimage forming apparatus forms a detection image on a belt and recreatesa γ curve to correct the look-up table (see, for example, JapanesePatent Application Laid-Open No. H08-227222).

In recent years, there has been a demand for image forming apparatusexhibiting further improved image quality, and there is a color gamut asone of indicators thereof. The color gamut in the image formingapparatus refers to a color reproduction range that can be output by theimage forming apparatus, and means that, as the color gamut becomeswider, the color reproduction range becomes wider and superiorityincreases as the image forming apparatus. For example, a method ofincreasing a developer amount on a recording material is conceivable asone method of expanding the color gamut. In Japanese Patent ApplicationLaid-Open No. H08-227222, there is disclosed a proposal for adjusting acolor impression of a secondary color by changing a rotation speed of adeveloping roller. The configuration of Japanese Patent ApplicationLaid-Open No. H08-227222 has an object to adjust the color impression,and is not intended to increase the developer amount on the recordingmaterial, but this technology can be utilized to expand the color gamut.That is, it is possible to increase the developer amount by increasingthe rotation speed of the developing roller.

However, the related art has the following problem in terms of formationof the detection image. When the rotation speed of the developing rollerand other such process conditions are changed, it is required to formand detect the detection image for each of the process conditions.However, downtime increases when the detection image is formed anddetected for each process condition each time the process condition ischanged.

SUMMARY

In order to solve the above-mentioned problem, according to oneembodiment of the present disclosure, there is provided an image formingapparatus, comprising:

a photosensitive drum;

a developing roller configured to develop an electrostatic latent imageon the photosensitive drum with a toner to form a toner image;

a belt onto which the toner image formed on the photosensitive drum isto be transferred or on which a recording material, onto which the tonerimage is to be transferred, is borne;

a detector configured to detect a density of a detection image formed onthe belt, wherein the image forming apparatus is configured to performan image formation in a first mode in which a circumferential speeddifference of a circumferential speed of the developing roller withrespect to a circumferential speed of the photosensitive drum is a firstcircumferential speed difference and in a second mode in which thecircumferential speed difference is larger than the firstcircumferential speed difference;

a controller configured to calculate a first conversion unit configuredto convert a gradation of an input image data so that a density outputfor the input image data becomes a first density output characteristicbased on a first detection result of the detection image detected by thedetector in the first mode; and

a storage,

wherein the controller is configured to generate a second conversionunit configured to convert the gradation of the input image data so thatthe density output for the input image data becomes a second densityoutput characteristic in the second mode based on the detection resultin the first mode and correction information, and

wherein the controller is configured to further update the correctioninformation based on a second detection result of the detection imagedetected by the detector in the second mode and the first detectionresult.

According to another embodiment of the present disclosure, there isprovided an image forming apparatus, comprising:

a photosensitive drum;

a developing roller configured to develop an electrostatic latent imageon the photosensitive drum with a toner to form a toner image;

a belt onto which the toner image formed on the photosensitive drum isto be transferred or on which a recording material, onto which the tonerimage is to be transferred, is borne;

a detector configured to detect a density of a detection image formed onthe belt;

a controller configured to perform a first detection image actualmeasurement for obtaining a first characteristic indicating arelationship between an input image data in a first mode and a densitycorresponding to the input image data based on a result of detecting thedensity of the detection image by the detector in the first mode; and

a storage,

wherein the controller is configured to perform a predicted densitycorrection for predicting, based on the first characteristic, acharacteristic indicating a relationship between an input image data ina second mode in which an image formation is performed with a colorgamut different from a color gamut in the first mode and the densitycorresponding to the input image data, and perform an image formation inthe second mode by using a predicted characteristic,

wherein the controller is configured to perform a second detection imageactual measurement for obtaining a second characteristic indicating arelationship between the input image data in the second mode and thedensity corresponding to the input image data based on a result ofdetecting the density of the detection image by the detector in thesecond mode, obtain a correction value based on the secondcharacteristic and the predicted characteristic, and correct thepredicted characteristic by using an obtained correction value whilestoring the obtained correction value in the storage, and

wherein the controller is configured to further correct the predictedcharacteristic by using the obtained correction value stored in thestorage without performing the second detection image actualmeasurement.

Further features of the present disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an image formingapparatus according to a first embodiment and a second embodiment of thepresent disclosure to be disclosed.

FIG. 2A is a schematic configuration diagram of an image forming stationin each of the first embodiment and the second embodiment to bedisclosed.

FIG. 2B is a schematic explanatory diagram of a layer structure of aphotosensitive drum.

FIG. 3 is a schematic explanatory graph of a surface potential of thephotosensitive drum in the first embodiment to be disclosed.

FIG. 4A is a schematic explanatory diagram of a configuration of adensity sensor in each of the first embodiment and the second embodimentto be disclosed.

FIG. 4B and FIG. 4C are each a schematic explanatory graph of a densitysensor output.

FIG. 5 is a schematic explanatory diagram of controller processing ineach of the first embodiment and the second embodiment to be disclosed.

FIG. 6A is a schematic explanatory graph of a look-up table at the timeof a normal print mode in the first embodiment to be disclosed.

FIG. 6B is a schematic explanatory graph of a look-up table at the timeof a wide color gamut print mode.

FIG. 7A and FIG. 7B are each a schematic explanatory graph of densitiesbased on a circumferential speed of a developing roller and a degree ofuse of the photosensitive drum in the first embodiment to be disclosed.

FIG. 8A is a schematic explanatory graph of the surface potential withrespect to a light intensity based on the degree of use of thephotosensitive drum in the first embodiment to be disclosed.

FIG. 8B is a schematic explanatory graph of densities based on a degreeof use of a developing unit.

FIG. 9 is a schematic explanatory graph of density ratios between thenormal print mode and the wide color gamut print mode in the firstembodiment to be disclosed.

FIG. 10 is a flow chart for illustrating a control method for densitycorrection in the first embodiment to be disclosed.

FIG. 11A and FIG. 11B are each a graph for showing a γ curve obtained byverification in the first embodiment to be disclosed.

FIG. 12 is a flow chart for illustrating a control method for densitycorrection in the second embodiment to be disclosed.

FIG. 13 is a graph for showing a γ curve obtained by verification in thesecond embodiment to be disclosed.

FIG. 14 is a flow chart for illustrating a control method for densitycorrection in the third embodiment to be disclosed.

DESCRIPTION OF THE EMBODIMENTS

Now, modes for carrying out the present disclosure will be described asembodiments with reference to the accompanying drawings.

First Embodiment

[Image Forming Apparatus]

FIG. 1 is a schematic configuration diagram of an image formingapparatus 200 according to a first embodiment of the present disclosure.The image forming apparatus 200 is a full-color laser printer thatemploys an in-line system and an intermediate transfer system. The imageforming apparatus 200 is also an image forming apparatus capable offorming an image in a normal print mode being a first mode and in a widecolor gamut print mode being a second mode using a color gamut differentfrom a color gamut in the normal print mode. The image forming apparatus200 forms a full-color image on a recording material 203 serving as atransfer material based on image information input from a host computer(hereinafter referred to as “host PC”) (not shown) to an enginecontroller 202 via a controller 201. The image forming apparatus 200includes a nonvolatile memory 230 serving as a storage, and thecontroller 201 stores information including a difference ΔL(i), which isdescribed later, in the nonvolatile memory 230.

The image forming apparatus 200 includes image forming stations SY, SM,SC, and SK for respective colors. As an example, the image formingstation SY for yellow is illustrated in FIG. 2A. The image formingstation SY includes a process cartridge 204Y, an intermediate transferbelt 205 configured to be rotated in an arrow-A direction illustrated inFIG. 2A, and a primary transfer roller 206Y arranged on a side oppositeto the process cartridge 204Y across the intermediate transfer belt 205.The arrow-A direction illustrated in FIG. 2A is hereinafter referred toas “rotation direction A”. The process cartridge 204Y includes anonvolatile memory 234Y. The nonvolatile memory 234Y stores, forexample, a current use amount of a toner (hereinafter referred to as“toner use amount”), a current use amount of the drum unit 310, or othersuch pieces of information. Those pieces of information stored in thenonvolatile memory 234Y are successively updated each time printing isperformed. The respective image forming stations SY, SM, SC, and SK arearranged in alignment with each other in the rotation direction A of theintermediate transfer belt 205, and are substantially the same as oneanother except for the color of an image to be formed. Therefore, unlessotherwise distinguished from one another, the respective image formingstations SY, SM, SC, and SK are collectively described by omitting thesuffixes Y, M, C, and K each indicating that the component is providedfor the corresponding color.

The process cartridge 204 includes a photosensitive drum 301 serving asan image bearing member. The photosensitive drum 301 is rotationallydriven in an arrow-B direction illustrated in FIG. 2A by a drive unit(not shown). A charging roller 302 has a high voltage applied by ahigh-voltage power supply (not shown), to thereby uniformly charge thesurface of the photosensitive drum 301. Then, a scanner unit 207 servingas an exposure unit irradiates the photosensitive drum 301 with laserlight based on the image information input to the engine controller 202,to thereby form an electrostatic latent image on the surface of thephotosensitive drum 301. A developing roller 303 serving as a developersupply unit is rotated in an arrow-C direction illustrated in FIG. 2A bya drive unit (not shown). Toner serving as developer, which has beencharged to coat the surface of developing roller 303, adheres along theelectrostatic latent image on the surface of the photosensitive drum301, to thereby cause the electrostatic latent image to become a visibleimage. In the following description, the visible image based on thetoner is referred to as “toner image”.

A base layer of the photosensitive drum 301 is grounded, and a voltagehaving a polarity reverse to that of the toner is applied to the primarytransfer roller 206 by a high-voltage power supply (not shown).Therefore, an electric field is formed at a nip portion formed betweenthe primary transfer roller 206 and the photosensitive drum 301, and thetoner image is transferred from the photosensitive drum 301 onto theintermediate transfer belt 205. The intermediate transfer belt 205 isstretched around an opposing roller 217 as well, and a density sensor218, which serves as a detection unit, is provided on a side opposite tothe opposing roller 217 across the intermediate transfer belt 205.

The toner remaining on the surface of the photosensitive drum 301 thatcannot be completely transferred onto the intermediate transfer belt 205is removed from the photosensitive drum 301 by a drum cleaning blade 304to be collected in a waste toner container 305. A toner replenishingroller 306 is rotated in an arrow-D direction illustrated in FIG. 2A toreplenish the developing roller 303 with the toner, and a stirrer 307 isrotated in an arrow-E direction illustrated in FIG. 2A to replenish thetoner replenishing roller 306 with the toner. A toner regulating blade308 is fixed, and hence the developing roller 303 is rubbed by the tonerregulating blade 308 due to its own rotation. The toner coating thesurface of the developing roller 303 has the amount regulated whilebeing charged at this rubbing portion. As a result, the toner image canbe developed with a stable density. A configuration including thedeveloping roller 303, the stirrer 307, the toner replenishing roller306, and the toner regulating blade 308 is hereinafter referred tocollectively as “developing unit 309”. Meanwhile, a configurationincluding the photosensitive drum 301, the charging roller 302, the drumcleaning blade 304, and the waste toner container 305 is hereinafterreferred to collectively as “drum unit 310”.

The image forming apparatus 200 according to the first embodiment cannot only use the normal print mode as a reference image formation modebut also use the wide color gamut print mode as a variable density imageformation mode. In the wide color gamut print mode, a difference of thecircumferential speed (hereinafter referred to as “circumferential speeddifference”) of the developing roller 303 from the circumferential speedof the photosensitive drum 301 is set larger than in the normal printmode, or the potential contrast is increased so that a developer amountper unit area on the photosensitive drum 301 (on a photosensitive drum)is increased to achieve a wider color gamut. In the following, thedeveloper amount is also referred to as “toner amount”. That is, in thewide color gamut print mode, the circumferential speed difference isincreased so that the supply amount of toner becomes larger than in thenormal print mode. This requires the setting of the surface potential ofthe photosensitive drum 301, and setting of the potential contrast isdescribed later in detail.

The intermediate transfer belt 205 is rotated in the rotation directionA, to thereby cause toner images generated in the image forming stationsS for the respective colors to be formed on the intermediate transferbelt 205 (on the belt) and carried. The recording materials 203 arereceived to be stacked in a sheet feeding cassette 208. Sheet feedingrollers 209 are driven based on a sheet feeding start signal, to therebyfeed each of the recording materials 203. The recording material 203 isconveyed so as to reach, via a registration roller pair 210, the nipportion (hereinafter also referred to as “secondary transfer portion”)formed between a secondary transfer roller 211 and a secondary transferopposing roller 212 at a predetermined timing.

Specifically, the recording material 203 is conveyed so that the leadingedge portion of the toner image on the intermediate transfer belt 205and the leading edge portion of the recording material 203 meet eachother at a predetermined timing. While the recording material 203 isnipped and conveyed between the secondary transfer roller 211 and thesecondary transfer opposing roller 212, a voltage having a polarityreverse to that of the toner is applied to the secondary transfer roller211 from a power supply apparatus (not shown). The secondary transferopposing roller 212 is grounded, and hence an electric field is formedbetween the secondary transfer roller 211 and the secondary transferopposing roller 212. This electric field causes the toner image to betransferred from the intermediate transfer belt 205 onto the recordingmaterial 203. After passing through the nip portion between thesecondary transfer roller 211 and the secondary transfer opposing roller212, the recording material 203 is subjected to heating and pressurizingprocessing by a fixing device 213. This causes the toner image on therecording material 203 to be fixed to the recording material 203. Afterthat, the recording material 203 is conveyed from an outlet 214 to adelivery tray 215, and thus the process of image formation is completed.Meanwhile, the toner on the intermediate transfer belt 205 that cannotbe completely transferred by the secondary transfer portion is removedfrom the intermediate transfer belt 205 by a cleaning member 216, andthe intermediate transfer belt 205 is refreshed to a state that allowsthe image formation again.

The image forming apparatus 200 includes an operating unit 300. Theoperating unit 300 includes a numeric keypad or a touch panel. On theoperating unit 300, information relating to printing is received asinput from a user, and information indicating a state of the imageforming apparatus 200 is displayed.

[Photosensitive Drum]

FIG. 2B is a diagram for illustrating a layer structure of thephotosensitive drum 301. The photosensitive drum 301 is structured oflayers in order from the bottom layer as follows. The photosensitivedrum 301 is formed of a drum base 311 made of aluminum or other suchconductive material, an undercoat layer 312 for suppressing theinterference of light and improving the adhesive property of an upperlayer, a charge generating layer 313 for generating a carrier, and acharge transporting layer 314 for transporting the generated carrier.The drum base 311 is grounded, and the surface of the photosensitivedrum 301 is charged by the charging roller 302 so that an electric fielddirected from the inside of the photosensitive drum 301 toward theoutside is formed. When the photosensitive drum 301 is irradiated withlaser light L by the scanner unit 207, a carrier (circle with a plussign) is generated by the charge generating layer 313. This carrier ismoved by the above-mentioned electric field (broken line) to be pairedwith a charge (circle with a minus sign) on the surface of thephotosensitive drum 301, to thereby change the surface potential of thephotosensitive drum 301.

[Surface Potential of Photosensitive Drum or the Like]

The surface potential of the photosensitive drum 301 in the normal printmode and the wide color gamut print mode is described with reference toFIG. 3. In FIG. 3, the vertical axis represents a potential (−V). First,the potential to which the surface of the photosensitive drum 301 ischarged by the charging roller 302 is set as a charging potential Vd.After that, the surface potential of the photosensitive drum 301, whichhas been exposed to light, is changed to an exposure potential Vl. Avoltage is applied to the developing roller 303 by a high-voltage powersupply (not shown) so as to maintain a developing potential Vdc. Thedeveloping potential Vdc is set between the exposure potential Vl andthe charging potential Vd. Therefore, in a non-exposure section, anelectric field is formed in a direction reverse to a direction in whichthe toner coating the surface of the developing roller 303 is developedtoward the photosensitive drum 301 side, while in an exposure section,an electric field is formed in the direction in which the toner isdeveloped toward the photosensitive drum 301 side. The toner isdeveloped in the exposure section based on the electric field, but thesurface potential of the photosensitive drum 301 increases due to atoner charge as more toner is developed, and hence the electric fieldbecomes weaker in the exposure section. Therefore, even when thecircumferential speed difference is increased with the aim of increasinga toner supply amount, the toner amount on the photosensitive drum 301is saturated with a certain circumferential speed difference. In orderto increase the toner amount on the photosensitive drum 301, it isrequired to set a sufficient potential contrast (Vdc−Vl). In this case,the potential contrast of Vdc−Vl is set as a potential contrast Vcont.However, even when the exposure amount is increased under a state inwhich the charges based on the charging voltage have sufficientlydisappeared due to the exposure, the electric field inside thephotosensitive drum 301 has become weaker, and hence the carriergenerated in the charge generating layer 313 is not moved to thesurface, which inhibits the potential from being changed. Therefore, inorder to set a higher potential contrast Vcont, a higher chargingvoltage is required.

As described above, in the normal print mode for a construction of thefirst embodiment, a circumferential speed difference of 140%, Vd_n=−500V, Vdc_n=−350 V, and Vl_n=−100 V are employed. Meanwhile, in the widecolor gamut print mode, the circumferential speed difference of 280%,Vd_w=−850 V, Vdc_w=−600 V, and Vl_w=−120 V are employed. In this case,the charging voltage Vd, the developing potential Vdc, and the exposurepotential Vl are represented by Vd_n, Vdc_n, and Vl_n, respectively, inthe normal print mode, and represented by Vd_w, Vdc_w, and Vl_w,respectively, in the wide color gamut print mode. Each of the potentialsin each print mode is set to a sufficient value required for developingthe toner coating the surface of the developing roller 303. Therefore,even when the potential fluctuates for some reason, the toner amount tobe developed does not change, which stabilizes the density. However,assuming that each of the potentials in the wide color gamut print modeis employed in the normal print mode, when the potential fluctuates, thetoner amount to be developed changes in accordance with the fluctuation,which impairs the stability of the density. As described above, in thefirst embodiment, Vd_n, Vdc_n, and Vl_n are employed, instead of Vd_w,Vdc_w, and Vl_w, as the respective potentials in the normal print modefrom the viewpoint of the stability of the density.

[Density Sensor]

In an electrophotographic image forming apparatus, the hue of printedmatter varies depending on various conditions including the use state ofthe cartridge and the use environment. Therefore, it is required tomeasure the density as appropriate and feed back the density to acontrol mechanism inside an image forming apparatus main body. FIG. 4Ais a diagram for illustrating a schematic configuration of the densitysensor 218 serving as a density measuring unit. After having beentransferred onto the surface of the intermediate transfer belt 205 inthe image forming station S, a toner image T is carried to the positionof the opposing roller 217 in accordance with the rotation of theintermediate transfer belt 205. The density sensor 218 is arranged on aside opposite to the opposing roller 217 across the intermediatetransfer belt 205. The density sensor 218 mainly includes a lightemitting element 219, a specularly-reflected-light receiving element220, and a diffusely-reflected-light receiving element 221. The lightemitting element 219 emits infrared light, and the infrared light isreflected by the surface of the toner image T. Thespecularly-reflected-light receiving element 220 is arranged in aspecular reflection direction with respect to the position of the tonerimage T, and detects light specularly reflected at the position of thetoner image T. The diffusely-reflected-light receiving element 221 isarranged at a position other than a position in the specular reflectiondirection with respect to the toner image T, and detects light diffuselyreflected at the position of the toner image T. The rotation direction Ain FIG. 4A is the same as the above-mentioned rotation direction A ofthe intermediate transfer belt 205, and in FIG. 4A, the intermediatetransfer belt 205 is moved from the back of the drawing sheet toward thefront.

[Sensor Output]

FIG. 4B is a graph for showing output results obtained by the densitysensor 218. In FIG. 4B, the horizontal axis represents image data, whichis expressed in hexadecimal (Hex), and the vertical axis represents anoutput (sensor output) from the density sensor 218. When the toner imageT has a small toner amount, that is, when the image data has a smallvalue, the density sensor 218 detects the reflection from the surface ofthe intermediate transfer belt 205, which is smooth, mirror finished,and black, and hence a specular reflection detecting output 401 (dottedline) is large, while a diffuse reflection detecting output 402 (brokenline) is small. The particle diameter of the toner is larger than thescale of the surface properties of the intermediate transfer belt 205.Therefore, when the toner is increased, that is, when the image data hasa larger value, the specular reflection detecting output 401 becomessmaller, while the diffuse reflection detecting output 402 becomeslarger. The specular reflection detecting output 401 includes a diffusereflection component, and hence it is possible to obtain a sensor output403 (solid line) correlated with the density by subtracting the diffusereflection component from the specular reflection detecting output 401based on the diffuse reflection detecting output 402. As describedabove, the density is calculated based on the detection results of thespecularly reflected light and the diffusely reflected light, which areobtained by the density sensor 218.

[Diffused Reflection Detection Output]

Through use of the sensor output described above, it is possible tomeasure a detection image in the wide color gamut print mode. However,when a toner amount of the detection image (detection image having alarge gradation value) increases, accuracy of the above-mentioned sensordeteriorates. Now, a mechanism for improving the accuracy by correctingthe diffused reflection detection output 402 with the specularreflection detection output (after diffuse reflection output issubtracted) 403 is described. Details thereof are described in, forexample, Japanese Patent Application Laid-Open No. 2002-236402.

FIG. 4C is a graph for showing the specular reflection detection output(after diffuse reflection output is subtracted) 403 and the diffusedreflection detection output 402, which are exhibited when the tonerimage T on the surface of the intermediate transfer belt 205 is detectedby the density sensor 218. The horizontal axis represents a density, andthe vertical axis represents a detection output. In this case, thedetection output obtained when a yellow toner is detected by the densitysensor 218 is described as an example. The specular reflection detectionoutput 403 is detected by the density sensor 218 at a predeterminedtiming. The diffused reflection detection output 402 is detected by thedensity sensor 218 at the same predetermined timing as that of thespecular reflection detection output 403. The specular reflectiondetection output 403 has the highest detection output when detecting thesurface of the intermediate transfer belt 205 (namely, when the densityis 0). Meanwhile, the specular reflection detection output 403 has thedetection output reaching to stay at a lower limit of 0 around aposition at which the density becomes 1. It is understood therefrom thatthe specular reflection detection output 403 exhibits high detectionaccuracy on the low density side, while exhibiting low detectionaccuracy on the high density side.

The diffused reflection detection output 402 rises as the densityincreases. It is understood that the detection accuracy is inferior dueto a smaller change in value than in the case of the specular reflectiondetection output 403 on the low density side, but satisfactory detectionaccuracy is exhibited on the high density side. In view of this, densitydetection is performed on the high density side with normalized diffusedreflection detection output, to thereby be able to improve accuracy ofdensity detection.

Now, a normalization correction procedure for the diffused reflectiondetection output using the specular reflection detection output isdescribed with reference to FIG. 4C. First, the specular reflectiondetection output 403 normalized by a base output value is uniquelydetermined, and hence in the first embodiment, the detection output at adensity of 0.5 is set as a reference value P. In FIG. 4C, the diffusedreflection detection output 402 that has not been normalized is set asP1 at the density of 0.5.

Therefore, the diffused reflection detection output 402 that has notbeen normalized is multiplied by the value of P/P1 to obtain diffusedreflection detection output 404 that has been normalized. Then, thecontroller 201 detects and acquires the diffused reflection detectionoutput 404 through the detection of the detection image having agradation equal to or higher than a predetermined density (equal to orhigher than a density of, for example, 0.5).

The diffused reflection detection output 404 that has been normalizedcan be obtained by the above-mentioned procedure, to thereby allow moreaccurate density detection to be performed even in a high density region(exhibiting a density equal to or higher than, for example, 0.5).

[Image Processing]

Next, it is described how hue information obtained by the density sensor218 is used for correction. In FIG. 5, an outline of a flow ofprocessing of the controller is illustrated. In general, a print jobdescribed in PCL, PostScript, or other such page description language(PDL) is transmitted from the host PC 222 or the like to the controller201. The controller 201 transmits bitmap information on Y, M, C, and Kto the engine controller 202 mainly via a raster image processor (RIP)portion 223, a color conversion portion 224, a γ correction portion 225,and a halftoning portion 226.

Specifically, the RIP portion 223 subjects the print job described inPDL, which has been transmitted from the host PC 222, to a file analysisby an interpreter, and performs conversion into an RGB bitmapcorresponding to the resolution of the image forming apparatus 200. Ingeneral, a color reproduction range of the electrophotographic imageforming apparatus is narrower than a color reproduction range of aliquid crystal display. Therefore, the color conversion portion 224 inthe subsequent stage performs color matching so as to match the hue asmuch as possible in consideration of a difference in color reproductionrange between devices. The color conversion portion 224 also performs,for example, conversion from RGB data into YMCK data. After that, the γcorrection portion 225 performs gamma correction, and the halftoningportion 226 performs dithering or other such gradation expressionprocessing. The detection results obtained by the density sensor 218 areused for selecting appropriate image data by the γ correction portion225.

[Lookup Table]

In FIG. 6A, a lookup table (LUT) is shown. In the first quadrant of FIG.6A, a graph of a lookup table is shown, and the horizontal axisrepresents input image data, which is expressed in hexadecimal (Hex),while the vertical axis represents image data to be used, which isexpressed in hexadecimal. In the second quadrant of FIG. 6A, a γ curvebefore correction (hereinafter also referred to as “before-correctionγ-curve”) is shown, and the horizontal axis represents a reflectiondensity, while the vertical axis represents the image data to be used inthe same manner as in the first quadrant. The reflection density is alsoreferred to simply as “density”. The γ curve refers to a curved lineindicating a relationship between input image data (i) and an actualoutput image density corresponding to the input image data. In the thirdquadrant, a γ curve after correction (hereinafter also referred to as“after-correction γ curve”) is shown, and the horizontal axis representsthe reflection density (density output) in the same manner as in thesecond quadrant, while the vertical axis represents the input image data(Hex). The graph shown in the second quadrant of FIG. 6A is thebefore-correction γ-curve. Normally, the before-correction γ-curve hasno linearity. Therefore, the input image data is not used as it is, andsuch image data as to maintain linearity is selected to be used. A tableindicating a correlation between this input image data and the imagedata to be actually used is referred to as “lookup table”. In addition,processing for recreating the lookup table based on the characteristicof the current image forming apparatus main body is referred to as“gamma correction” (hereinafter referred to as “γ correction”). It isassumed to be ideal that, as shown in the third quadrant of FIG. 6A,there is linearity in a relationship between the input image data andthe reflection density. This graph is a graph for showing a generalrelationship between the input image data and the reflection density andthe like. The data of this graph is, for example, data obtained based ona result of measuring the density of an image after fixation, which hasbeen printed on the recording material 203, by an external measuringapparatus or the like. For example, it is understood in this examplethat it is actually required to use the image data of C0h in order toobtain an ideal density for the input image data of 80h in considerationof the characteristic (before-correction γ-curve) of the current imageforming apparatus main body shown in the second quadrant of FIG. 6A.

The before-correction γ-curve is the characteristic of the current imageforming apparatus itself, and varies depending on various conditionsincluding the cartridge and the use environment. The same applies to adifference between print modes, for example, the normal print mode andthe wide color gamut print mode. A graph of FIG. 6B is plotted in thesame manner as in the graph of FIG. 6A, and descriptions of thehorizontal axis, the vertical axis, and the like are omitted. FIG. 6B isa graph for showing how the reflection density deviates from thelinearity when printing is performed in the wide color gamut print modethrough use of the lookup table (first conversion unit) optimized forthe normal print mode. In FIG. 6B, the broken line in the secondquadrant indicates the characteristic of the image forming apparatusmain body in the normal print mode, and the graph of the broken line isthe same as the graph of the second quadrant of FIG. 6A. Meanwhile, inFIG. 6B, the solid line in the second quadrant indicates thecharacteristic (before-correction γ-curve) of the image formingapparatus main body in the wide color gamut print mode. The wide colorgamut print mode is a print mode of increasing the toner amount byincreasing the circumferential speed difference of the developing roller303 from the photosensitive drum 301. Therefore, in the wide color gamutprint mode, the reflection density is higher than in the normal printmode over the entire image data area. When the image formation isperformed based on the input image data of 80h, the reflection densityis about 0.6 in the normal print mode, while the reflection densityincreases to 1.0 in the wide color gamut print mode. That is, when theLUT in the normal print mode is used for the input image data of 80h,the image data to be used becomes C0h. For this reason, the density inthe wide color gamut print mode becomes 1.0, which is darker than 0.6being the density to be achieved.

As a result, as shown in the third quadrant of FIG. 6B, theafter-correction γ-curve (broken line) in the normal print mode haslinearity, while the after-correction γ-curve (solid line) in the widecolor gamut print mode does not have linearity, and has a lopsidedshape. Therefore, it is normally required to obtain a lookup table inthe wide color gamut print mode after grasping the gamma through use ofthe density sensor 218 also in the wide color gamut print mode in thesame manner as in the normal print mode. However, in order to obtain theLUT for the wide color gamut print mode, it is required to add the stepof forming a toner image (detection image) for detection on theintermediate transfer belt 205 and measuring the density of the tonerimage for detection by the density sensor 218 also in the wide colorgamut print mode separately from the normal print mode. This causesdowntime for obtaining a LUT in the wide color gamut print mode.

[Regarding Predicted Density Correction]

In the first embodiment, detection image actual measurement that causesdowntime with satisfactory accuracy is combined with predicted densitycorrection that causes no downtime with accuracy lower than that of thedetection image actual measurement. With this combination, the frequencyof performing the detection image actual measurement can be suppressedwhile a stable color impression is reproduced. The predicted densitycorrection in the first embodiment is described. In the predicteddensity correction, the γ correction is performed by creating a look-uptable in the wide color gamut print mode based on predeterminedinformation and density information in the normal print mode. Thepredetermined information includes, for example, a circumferential speeddifference of the developing roller 303 from a photosensitive drum 301and information relating to the use of the cartridge. Now, parameters(predetermined information described above) required when the densityinformation in the wide color gamut print mode is calculated from thedensity information in the normal print mode are described.

[Circumferential Speed Difference of Developing Roller 303]

FIG. 7A is a graph for showing a density exhibited when thecircumferential speed difference is changed under potential settings inthe wide color gamut print mode, namely, Vd_w=−850 V, Vdc_w=−600 V, andVl_w=−120 V In FIG. 7A, the horizontal axis represents the image data,and the vertical axis represents the density (OD). The data is obtainedwhen the circumferential speed difference is 140%, 200%, 240%, and 280%.It is understood that, in any gradation (image data), the densitybecomes higher as the circumferential speed difference becomes larger.As has been described so far, this is because the toner amount suppliedto the photosensitive drum 301 is increased by increasing thecircumferential speed difference. Therefore, in order to calculate thedensity information in the wide color gamut print mode from the densityinformation in the normal print mode, it is required to include thecircumferential speed difference as one of the parameters.

[Degree of Use of Photosensitive Drum 301]

FIG. 7B is a graph for showing differences in density in the wide colorgamut print mode among drum units exhibiting different degrees of use.The horizontal axis and the vertical axis of FIG. 7B are the same asthose of FIG. 7A, and descriptions thereof are omitted. A drum unit 310Ais in a new condition, a drum unit 310B has printed 20,000 recordingmaterials 203, and a drum unit 310C has printed 50,000 recordingmaterials 203. As the number of printed recording materials 203 becomeslarger, that is, as the use of the photosensitive drum 301 progresses,the density becomes lower (lighter) over the entire image data area.This is because the sensitivity of the photosensitive drum 301 to alight amount of light emitted by the scanner unit 207 is changed due tothe use.

FIG. 8A is a graph for showing a concept of the characteristics of thelight amount of the light emitted by the scanner unit 207 and thesurface potential of the photosensitive drum 301. In FIG. 8A, thehorizontal axis represents the light amount of the light emitted by thescanner unit 207, and the vertical axis represents the surface potential(−V) of the photosensitive drum 301. In FIG. 8A, a new photosensitivedrum 301A and an (old) photosensitive drum 301B exhibiting a largedegree of use are shown. The photosensitive drum 301 becomes thinner inthickness as the charge transporting layer 314 being the outermost layerof the photosensitive drum 301 is scraped more due to the use. Acapacitance increases as the photosensitive drum 301 becomes thinner inthickness, and hence the sensitivity for the surface potential to anamount of charge by which the surface is charged becomes lower.Therefore, when exposure is to be performed to lower the potential to anexposure potential Vl0, which is the same as that of the newphotosensitive drum 301A, a light amount La is sufficient for the newphotosensitive drum 301A, but the old photosensitive drum 301B requiresa larger light amount Lb (Lb>La). This means that, in order to achievethe same density as the density achieved by the new photosensitive drum301A, the old photosensitive drum 301B requires the image data having ahigher density.

As described above, it is understood that the density depends on thenumber of printed recording materials 203 that have been printed by thedrum unit 310. As understood from the data shown in FIG. 7B, the drumunit 310B is plotted substantially in the middle between the drum unit310A and the drum unit 310C, and hence there is considered to be alinear correlation between a change in density due to the printingperformed on the recording material 203 and the number of printedrecording materials 203.

[Degree of Use of Developing Unit 309]

FIG. 8B is a graph for showing densities used by the developing units309 exhibiting different degrees of use in the wide color gamut printmode. The horizontal axis and the vertical axis of FIG. 8B are the sameas those of FIG. 7A and FIG. 7B, and descriptions thereof are omitted. Anew developing unit 309A exhibits a lower density over the entire imagedata area than a developing unit 309B subjected to the printing of 3,000recording materials 203 at a coverage rate of 5%. This is ascribable tothe fact that toner having a small particle diameter is relativelyeasily consumed at the beginning and is easily charged due to rubbingwith the toner regulating blade 308. As described above, as more toneris developed, a potential difference from Vdc decreases due to thecharge of the toner itself. This phenomenon is expressed as thepotential contrast Vcont (=Vdc-Vl) being gradually filled. As thepotential contrast Vcont is gradually filled with more toner charges,development is gradually performed less often. In higher charging, alarger part of the potential contrast Vcont is gradually filled, withthe result that the density is lowered. The term “high charging”mentioned above refers to being large in the minus direction, and thecharging becomes higher at a higher position on the vertical axis of thegraph of FIG. 3. Meanwhile, a developing unit 309C subjected to theprinting of 30,000 recording materials 203 at the same coverage rate of5% as that of the developing unit 309B exhibits a density substantiallythe same as that of the developing unit 309B. This is considered to bebecause, with the construction of the first embodiment, most of thetoner having a small particle diameter has been consumed at a timing atwhich about 3,000 recording materials 203 have been printed.

As described above, it is understood that the density depends on a toneruse amount. The toner use amount of toner used when 3,000 recordingmaterials 203 are printed at the coverage rate of 5% is a minute amountcompared to the whole toner amount. For this reason, it is assumed that,in the first embodiment, the density linearly changes until the toneruse amount equivalent to the amount of toner used when 3,000 recordingmaterials 203 are printed at the coverage rate of 5%, and after that,the density maintains a constant level without changing.

It is understood from FIG. 7A, FIG. 7B, and FIG. 8B that thecircumferential speed difference of the developing roller 303, thedegree of use of the drum unit 310, the consumption degree of the toner,and other such factor influence on a relationship between the densityinformation in the normal print mode and the density information in thewide color gamut print mode. Therefore, a correlation table between thedensity information in the normal print mode and the density informationin the wide color gamut print mode under each condition (predeterminedcondition) is provided in advance so that hue adjustment can beperformed without measuring the density in the wide color gamut printmode in addition to the normal print mode.

[Creation of Correlation Table]

Now, how the correlation table is created and how the correlation tableis applied are specifically described. Data required for creating thecorrelation table includes pieces of density data on the recordingmaterial 203 obtained in the normal print mode and the wide color gamutprint mode for the respective circumferential speed differences in thecase of using a new drum unit 310, a life-equivalent drum unit 310exhibiting a large degree of use, a new developing unit 309, and adeveloping unit 309 subjected to the printing of about 3,000 recordingmaterials 203 at the coverage rate of 5%. Those pieces of density dataare based on data obtained by measuring the density of the image afterthe fixation, which has been formed on the recording material 203, bythe external measuring apparatus or the like during, for example, adevelopment process for the image forming apparatus. In order to obtaina desired density in the image finally formed on the recording material203, the density of the image after the fixation, which has been formedon the recording material 203, is measured by the external measuringapparatus or the like. It is therefore assumed that a table indicating acorrelation between the data obtained by measuring the density of theimage after the fixation and data obtained by measuring the density ofan image before the fixation by the density sensor 218 is stored inadvance in, for example, a storage portion (not shown) included in thecontroller 201. As described above, the circumferential speed differenceis 280% in the wide color gamut print mode. FIG. 9 is a graph forshowing a correlation table for calculating the density at thecircumferential speed difference of 280% based on the densityinformation at the circumferential speed difference of 140% in thenormal print mode. In FIG. 9, the horizontal axis represents the imagedata (gradation), and the vertical axis represents a density ratio.

The correlation table refers to a density ratio between the two printmodes, and is defined as a quotient obtained by dividing the density inthe wide color gamut print mode by the density in the normal print mode.On a low density side (or a low gradation side or a side on which theimage data has a small value), the density in the normal print mode islow, and hence the density ratio tends to be high, and tends to becomesmaller as the density increases. In addition, the new drum unit 310Ahas a density ratio higher than that of the drum unit 310C using thephotosensitive drum 301 subjected to the printing of 50,000 recordingmaterials 203. This is ascribable to the fact that the drum units 310Aand 310C exhibit a larger difference between the densities in the widecolor gamut print mode than a difference between the densities in thenormal print mode. The difference between the densities in the widecolor gamut print mode is as described with reference to FIG. 7B.

When the density in the wide color gamut print mode is to be calculated,first, the current toner use amount is calculated based on the datastored in a nonvolatile memory 234 mounted to the process cartridge 204.As described above, the density linearly changes until the toner useamount (predetermined use amount) equivalent to the amount of toner usedwhen 3,000 recording materials 203 are printed at the coverage rate of5%, and after that, the density maintains a constant level. Therefore,the following item (1) is calculated from a correlation table 601 (firstdensity ratio) for the drum unit 310A and the developing unit 309A and acorrelation table 603 (second density ratio) for the drum unit 310A andthe developing unit 309B. That is, (1) a correlation table for the drumunit 310A and the current developing unit 309 is calculated. The toneruse amount is used for the calculation of the correlation table of theitem (1).

Specifically, when the current developing unit 309 has consumed thetoner having an amount equivalent to the amount of toner used when 3,000or more recording materials 203 are printed at the coverage rate of 5%,the correlation table for this case is the same as the correlation table603. Meanwhile, when the current developing unit has printed only lessthan 3,000 recording materials 203 at the coverage rate of 5%, thecorrelation table for this case falls in the middle between thecorrelation table 601 and the correlation table 603, and the correlationtable is calculated on the assumption that the change takes placelinearly based on the toner use amount.

In the same manner, the following item (2) is calculated from acorrelation table 602 (third density ratio) for the drum unit 310C andthe developing unit 309A and a correlation table 604 (fourth densityratio) for the drum unit 310C and the developing unit 309B. That is, (2)a correlation table for the drum unit 310C and the current developingunit 309 is calculated. Subsequently, the use amount of the current drumunit 310 is calculated based on the data stored in the nonvolatilememory 234 mounted to the process cartridge 204. Then, the correlationtable for the current drum unit 310 and the current developing unit iscalculated from the two correlation tables of (1) the correlation tablefor the drum unit 310A and the current developing unit 309 and (2) thecorrelation table for the drum unit 310C and the current developing unit309. The use amount of the drum unit 310 is used for the calculation ofthe correlation table of the item (2).

The influence of the use amount of the drum unit 310 on the density iscalculated on the assumption that the change takes place linearly basedon the use amount as described above. That is, the correlation table forthe drum unit 310 subjected to the printing of, for example, 25,000recording materials 203 falls right in the middle between thecorrelation table for the drum unit 310A and the current developing unitand the correlation table for the drum unit 310C and the currentdeveloping unit.

As described above, the image forming apparatus according to the firstembodiment uses the correlation table based on the density information(detection results obtained by the density sensor 218) in the normalprint mode and the circumferential speed difference of the developingroller 303 or other such parameter. With this configuration, the lookuptable in the wide color gamut print mode can be obtained withoutdowntime. In the first embodiment, the look-up table in the wide colorgamut print mode is obtained in the above-mentioned manner, and thepredicted density correction is performed by performing the γcorrection. Examples of parameters to be required other than thecircumferential speed difference include the degree of use of thephotosensitive drum 301 and the consumption degree of the toner. In theconstruction of the first embodiment, the circumferential speeddifference of the developing roller 303 is employed, but any parameterfor controlling the toner supply amount may be employed, and the presentdisclosure is not limited to the configuration using the circumferentialspeed difference. When the density information is changed by otherparameters, it is required to include those parameters as well. Specificexamples thereof include the rotation time of the developing roller 303.This is based on a phenomenon that the surface of the toner regulatingblade 308 wears due to the rubbing between the developing roller 303 andthe toner regulating blade 308 to change the amount of the toner coatingthe surface of the developing roller 303 after regulation.

In the first embodiment, the lookup table in the wide color gamut printmode is predicted based on the detection results obtained by the densitysensor 218 in the normal print mode. For example, the lookup table inthe normal print mode may be predicted based on the detection resultsobtained by the density sensor 218 in the wide color gamut print mode.The first mode and the second mode are herein described as the normalprint mode and the wide color gamut print mode. However, the predicteddensity correction can also be applied to an image forming apparatuscompatible with another print mode, for example, a toner saving printmode for suppressing toner consumption. In this case, the look-up tablein the toner saving print mode is predicted based on a detection resultobtained by the density sensor 218 in the normal print mode. The look-uptable in the normal print mode may be predicted based on a detectionresult obtained by the density sensor 218 in the toner saving printmode.

[Regarding Density Control in First Embodiment]

In the first embodiment, even when the toner amount is changed,predicted density correction information corrected by adding actualmeasurement information to predicted density correction information isused. In this case, the predicted density correction information refersto information obtained in the above-mentioned predicted densitycorrection, specifically, a before-correction γ curve (Lγpredicted(i)described later) based on the predicted density correction in the widecolor gamut print mode. The actual measurement information refers todifference information indicating a difference (ΔL(i) described later)between the before-correction γ curve based on the predicted densitycorrection and a before-correction γ curve (Lγdetected(i) describedlater) based on the detection image actual measurement in the wide colorgamut print mode, which is detected by the density sensor 218. With thisconfiguration, in the first embodiment, the frequency of performing thedetection image actual measurement can be suppressed while a stablecolor impression is reproduced. A control method in the first embodimentis described with reference to a flow chart illustrated in FIG. 10.After the description of the flow chart, effects of the first embodimentare verified.

When the image forming apparatus 200 is activated, the controller 201starts processing of Step S2 and the subsequent steps. In Step S2, thecontroller 201 performs the detection image actual measurement in thenormal print mode being first detection image actual measurement. Then,a before-correction γ curve Rγdetected(i) at the time of the normalprint mode is obtained, and a look-up table for achieving first densityoutput characteristics is also calculated by the controller 201. In thiscase, i represents input image data (for example, 40h or C0h). In StepS3, the controller 201 calculates the following value from suchcorrelation tables as shown in FIG. 7A, FIG. 7B, and FIG. 8B based onparameters including the circumferential speed difference of thedeveloping roller 303 exhibited when the detection image actualmeasurement is performed, the degree of use of the drum unit 310, andthe degree of toner consumption. That is, the controller 201 calculatesa correction value for the before-correction γ curve Rγdetected(i) inorder to obtain the before-correction γ curve in the wide color gamutprint mode based on the predicted density correction. The correctionvalue for correcting the before-correction γ curve Rγdetected(i) basedon the detection image actual measurement in the normal print mode ishereinafter expressed as ΔLpredicted(i).

When a before-correction γ curve indicating characteristics based on thepredicted density correction in the wide color gamut print mode isrepresented by Lγpredicted(i), Lγpredicted(i) is expressed by Expression(1).

Lγpredicted(i)=Rγdetected(i)+ΔLpredicted(i)  Expression (1)

In this case, the correction value ΔLpredicted can be obtained from FIG.7A, FIG. 7B, and FIG. 8B in the above-mentioned manner, and is furtherdescribed with reference to FIG. 6B. As described above, in the secondquadrant of FIG. 6B, the solid line indicates the before-correction γcurve in the wide color gamut print mode, and the broken line indicatesthe before-correction γ curve in the normal print mode, which are bothobtained from the density of a fixed image. In FIG. 6B, a correctionvalue ΔLγpredicted(i) corresponds to a difference between the twobefore-correction γ curves.

In Step S4, the controller 201 determines whether the difference ΔL(i)between the before-correction γ curve Lγdetected(i) based on thedetection image actual measurement in the wide color gamut print modeand the before-correction γ curve Lγpredicted(i) based on the predicteddensity correction in the wide color gamut print mode is stored in thenonvolatile memory 230. As described above, it is highly possible thatthe accuracy of the detection image actual measurement using the densitysensor 218 becomes higher than that of the predicted density correctionin which it is difficult to correct individual differences of the imageforming apparatus and the toner cartridge. It is preferred to use thestored difference ΔL(i) when the difference ΔL(i) calculated based onthe before-correction γ curve Lγdetected(i) in the wide color gamutprint mode based on the detection image actual measurement is stored inthe nonvolatile memory 230. The before-correction γ curve Lγpredicted(i)based on the predicted density correction in the wide color gamut printmode is corrected through use of the stored difference ΔL(i), to therebybe able to correct the individual differences of the image formingapparatus and the toner cartridge with high accuracy. In addition,through use of the difference ΔL(i) stored in nonvolatile memory 230, itis also possible to reduce the frequency of performing the detectionimage actual measurement in the wide color gamut print mode.

The difference ΔL(i) is expressed by Expression (2). The nonvolatilememory 230 may store the difference ΔL(i), or may store thebefore-correction γ curve Lγdetected(i) in the wide color gamut printmode based on the detection image actual measurement.

ΔL(i)=Lγdetected(i)−Lγpredicted(i)  Expression (2)

When determining in Step S4 the difference ΔL(i) is not stored in thenonvolatile memory 230, the controller 201 advances the processing toStep S5. In Step S5, the controller 201 performs the detection imageactual measurement in the wide color gamut print mode being seconddetection image actual measurement. The controller 201 performs thedetection image actual measurement in the wide color gamut print mode,to thereby calculate the before-correction γ curve Lγdetected(i). InStep S6, the controller 201 uses the above-mentioned Expression (2) tocalculate the difference ΔL(i). Specifically, the controller 201calculates the difference ΔL(i) from the before-correction γ curveLγdetected(i) in the wide color gamut print mode based on the detectionimage actual measurement, which is calculated in Step S5, and thebefore-correction γ curve Lγpredicted(i) in the wide color gamut printmode based on the predicted density correction, which is calculated inStep S3. The controller 201 stores the calculated difference ΔL(i) inthe nonvolatile memory 230. With this processing, the difference ΔL(i)stored in the nonvolatile memory 230 is used to correct thebefore-correction γ curve Lγpredicted(i) from the next time. Thisdifference ΔL(i) corresponds to the difference information.

In Step S7, the controller 201 corrects the before-correction γ curveLγpredicted(i) based on the predicted density correction in the widecolor gamut print mode. The controller 201 uses Expression (3) tocalculate the after-correction γ curve. The after-correction γ curvebased on the detection result in the wide color gamut print mode isrepresented by Lγcorrected(i).

Lγcorrected(i)=Lγpredicted(i)+ΔL(i)  Expression (3)

The look-up table for correcting the γ curve described in Expression (3)corresponds to a second conversion unit. In this manner, when thedifference ΔL(i) is not stored in the nonvolatile memory 230, thedetection image actual measurement in the wide color gamut print mode(Step S5) is performed along with the detection image actual measurementin the normal print mode (Step S2) and the predicted density correction(Step S3). For this reason, immediately after the detection image actualmeasurement is performed, Lγcorrected(i)=Lγdetected(i)(=Lγpredicted(i)+ΔL(i)=Lγpredicted(i)±(Lγdetected(i)−Lγpredicted(i))) isestablished. After that, the predicted density correction is performed,to thereby update the before-correction γ curve Lγpredicted(i) in thewide color gamut print mode, and also update Lγcorrected(i).

Meanwhile, when determining in Step S4 that the difference ΔL(i) isstored in the nonvolatile memory 230, the controller 201 advances theprocessing to Step S7. This occurs in a case where the detection imageactual measurement in the wide color gamut print mode was performed andthe difference ΔL(i) was stored in the nonvolatile memory 230 in Step S6in the past. In this case, the controller 201 avoids performing thedetection image actual measurement in the wide color gamut print mode.In Step S7, the controller 201 calculates Lγcorrected(i)(=Lγpredicted(i)+ΔL(i)) from the before-correction γ curveLγpredicted(i) in the wide color gamut print mode based on the predicteddensity correction, which is calculated in Step S3, and the differenceΔL(i) stored in the nonvolatile memory 230. In Step S8, when the userperforms the wide color gamut print mode, the controller 201 usesLγcorrected(i) calculated by Expression (3) of Step S7 to recreate alook-up table (second conversion unit) (to perform the γ correction),and performs image formation in the wide color gamut print mode. Atarget output density to be used when the look-up table (secondconversion unit) is created through use of Lγcorrected(i) by thecontroller 201 becomes second density output characteristics in contrastto the above-mentioned first density output characteristics.

In Step S9, the controller 201 determines whether a condition forperforming the detection image actual measurement in the normal printmode (illustrated as “performing condition”) has been satisfied. Whendetermining in Step S9 that the condition for performing the detectionimage actual measurement in the normal print mode has not beensatisfied, the controller 201 returns the processing to Step S8, anduses the result of the γ correction obtained in Step S8 to perform theimage formation in the wide color gamut print mode. When determining inStep S9 that the condition for performing the detection image actualmeasurement in the normal print mode has been satisfied, the controller201 returns the processing to Step S2 to perform the detection imageactual measurement in the normal print mode. In this case, the conditionfor performing the detection image actual measurement in the normalprint mode refers to a condition for a case in which there is a fearthat a color impression may be changed, for example, when the imageforming apparatus 200 has exceeded a predetermined number of printedsheets, when the cartridge is replaced, or when the use environment ischanged.

[Verification of Effects]

Verification as to how much difference occurs in the accuracy of densitycontrol was performed between the above-mentioned case in which thedensity control is performed by employing the control in the firstembodiment and a case in which the density control is performed by onlythe predicted density correction (based on control that does not involvethe correction using the difference ΔLpredicted(i)). For thisverification, a method of performing examination in the following orderunder the environment of a temperature of 23° C. and a humidity of 50%was employed.

[1] In the image forming apparatus 200, the detection image actualmeasurement in the normal print mode is performed to obtain thebefore-correction γ curve Lγpredicted(i) based on the predicted densitycorrection in the wide color gamut print mode (Step S3 of FIG. 10).

[2] The detection image actual measurement in the wide color gamut printmode is performed to obtain the before-correction γ curve Lγdetected(i)(Step S5 of FIG. 10).

[3] The difference ΔL(i) is obtained from the before-correction γ curveLγpredicted(i) in the wide color gamut print mode based on the predicteddensity correction ([1]) and the before-correction γ curve Lγdetected(i)in the wide color gamut print mode based on the detection image actualmeasurement ([2]) (Step S6 of FIG. 10).

[4] In order to cause a change in color impression of the image formingapparatus 200, 5,000 A4 sheets are printed with a coverage rate of 5%(change in color impression; Yes in Step S9 of FIG. 10).

[5] The detection image actual measurement in the normal print mode isagain performed to obtain a before-correction γ curveLγpredicted(5,000)(i) based on the predicted density correction in thewide color gamut print mode (Step S3 of FIG. 10). In this case, fordistinction from the before-correction γ curve Lγpredicted(i) of theitem [1], the before-correction γ curve obtained after the printing of5,000 sheets is expressed as Lγpredicted(5,000)(i). In addition,Lγcorrected(5,000)(i) (=Lγpredicted(5,000)(i)+ΔL(i)) corrected throughuse of the difference ΔL(i) obtained in the item [3] is calculated (Yesin Step S4 and Step S7 of FIG. 10).

[6] In order to verify accuracy, the detection image actual measurementin the wide color gamut print mode is again performed to obtain abefore-correction γ curve Lγdetected(5,000)(i). In this case, thebefore-correction γ curve obtained after the printing of 5,000 sheets isexpressed as Lγdetected(5,000)(i) for distinction from thebefore-correction γ curve Lγdetected(i) of the item [2].

[7] It is examined which of Lγpredicted(5,000)(i) obtained in the item[5] and Lγpredicted(5,000)(i)+ΔL(i) (=Lγcorrected(5,000)(i)) correctedbased on the difference ΔL(i) obtained in the item [3] is closer to thebefore-correction γ curve Lγdetected(5,000)(i) obtained in the item [6].

FIG. 11A is a graph for showing the before-correction γ curveLγpredicted(i) in the wide color gamut print mode based on the predicteddensity correction, the before-correction γ curve Lγdetected(i) in thewide color gamut print mode based on the detection image actualmeasurement, and the difference ΔL(i) that were obtained in theabove-mentioned items [1] to [3], respectively. In FIG. 11A, thehorizontal axis represents the input image data (i) with the verticalaxis representing the density on the recording material 203 (outputdensity), which applies to FIG. 11B referred to later. The curved lineindicated by the broken line and the sign “×” indicates thebefore-correction γ curve Lγpredicted(i) in the wide color gamut printmode based on the predicted density correction. The curved lineindicated by the solid line and the sign “o” indicates thebefore-correction γ curve Lγdetected(i) in the wide color gamut printmode based on the detection image actual measurement. The curved lineindicated by the dotted line and the solid sign “A” indicates thedifference ΔL(i) (=Lγdetected(i)−Lγpredicted(i)).

In the first embodiment, in the detection image actual measurement inthe normal print mode and the detection image actual measurement in thewide color gamut print mode, 17 patch toner images (detection images)obtained by changing the input image data are formed on the surface ofthe intermediate transfer belt 205 to be detected through use of thedensity sensor 218. Therefore, 17 points are plotted on each line(excluding the input image data of “0”). It is understood from FIG. 11Athat the before-correction γ curve Lγpredicted(i) in the wide colorgamut print mode based on the predicted density correction and thebefore-correction γ curve Lγdetected(i) in the wide color gamut printmode based on the detection image actual measurement match each other tosome extent, but partially deviate from each other.

Next, the before-correction γ curve Lγpredicted(5,000)(i) in the widecolor gamut print mode based on the predicted density correction, whichwas obtained in the items [5] to [7] after the image formation wasperformed on 5,000 recording materials 203 in the item [4], is shown inFIG. 11B. In addition, the before-correction γ curvesLγdetected(5,000)(i) in the wide color gamut print mode based on thedetection image actual measurement and Lγcorrected(5,000)(i)+ΔL(i) arealso shown in FIG. 11B. The curved line indicated by the broken line andthe sign “×” indicates the before-correction γ curveLγpredicted(5,000)(i) in the wide color gamut print mode based on thepredicted density correction. The curved line indicated by the solidline and the sign “o” indicates the before-correction γ curveLγdetected(5,000)(i) in the wide color gamut print mode based on anactual measurement density control. The curved line indicated by thedotted line and the solid sign “A” indicatesLγcorrected(5,000)(i)+ΔL(i). It is understood thatLγcorrected(5,000)(i)+ΔL(i), which was corrected through use of thedifference ΔL(i) obtained in the item [3], is closer to thebefore-correction γ curve Lγdetected(5,000)(i) based on the detectionimage actual measurement than the before-correction γ curveLγpredicted(5,000)(i) based on the predicted density correction. Fromthe above-mentioned result, it was successfully verified that, when thecontrol in the first embodiment is employed, a stable color impressioncan be reproduced while the frequency of performing the detection imageactual measurement is reduced.

In the first embodiment, the configuration for correcting thebefore-correction γ curve Lγdetected(i) based on the difference ΔL(i)has been described, but the present disclosure is not limited thereto.The difference between Lγdetected(i) and Rγdetected(i) may be set asMAO, and after that, Lγcorrected(i) may be obtained from Rγdetected(i)through use of this MAO. However, the difference ΔL(i) has a valuesmaller than that of the difference MAO, which is advantageous in thaterrors and variations due to environmental variations and other suchfactors are small. Further, in the first embodiment, when the differenceΔL(i) is not stored in the nonvolatile memory 230, the detection imageactual measurement in the wide color gamut print mode is performed tocalculate the difference ΔL(i). However, even when the difference ΔL(i)is stored in the nonvolatile memory 230, the detection image actualmeasurement in the wide color gamut print mode may be performed asrequired, to thereby calculate the difference ΔL(i) again.

According to the first embodiment described above, it is possible toreduce downtime relating to the formation and detection of the detectionimage.

Second Embodiment

A second embodiment of the present disclosure has a feature that, inaddition to the same control as in the first embodiment, the differenceΔL(i) is again calculated when image forming apparatus states are closerto each other between one exhibited at the time of performing thedetection image actual measurement and one exhibited at the time ofperforming the predicted density correction. In this case, the fact thatthe image forming apparatus states are closer to each other means thefollowing case. For example, a state in which 500 sheets have beenprinted by the same image forming apparatus from a given state A is setas a state B, and a state in which 1,000 sheets have been printed by thesame image forming apparatus from the state A is set as a state C. It isassumed that an environment involved under the states A and C is theenvironment of a temperature of 23° C. and a humidity of 50%, while anenvironment involved under the state B is the environment of atemperature of 10° C. and a humidity of 15%. On this assumption, thestate A is closer to the state C. In such a case, in the secondembodiment, even when the detection image actual measurement in the widecolor gamut print mode is performed under the state B, the value of thedifference ΔL(i) exhibited under the state A closer to the state C isemployed. The second embodiment is described below.

[Configuration of Image Forming Apparatus and Outlines of DetectionImage Actual Measurement and Predicted Density Correction]

Basic configurations and operations of the image forming apparatus, thedetection image actual measurement, and the predicted density correctionthat are to be used in the second embodiment are the same as thosedescribed in the first embodiment. Therefore, duplicate detaileddescriptions in the second embodiment are omitted. The second embodimentis different from the first embodiment in points relating to thecalculation of the difference ΔL(i) between the before-correction γcurve Lγdetected(i) based on the detection image actual measurement inthe wide color gamut print mode and the before-correction γ curveLγpredicted(i) based on the predicted density correction in the widecolor gamut print mode. In the first embodiment, when the nonvolatilememory 230 is not stored in the difference ΔL(i) after the detectionimage actual measurement in the normal print mode is performed, thedetection image actual measurement in the wide color gamut print mode issubsequently performed to calculate the difference ΔL(i). In that case,the accuracy of the difference ΔL(i) between the predicted densitycorrection and the detection image actual measurement in the wide colorgamut print mode is satisfactory, but the detection image actualmeasurement in the wide color gamut print mode is performed along withthe detection image actual measurement in the normal print mode, whichleads to a fear that long downtime may occur. Some users may wish toplace a higher priority on short downtime than on the accuracy ofdensity control, and hence it is conceivable to set a timing to performthe detection image actual measurement in the wide color gamut printmode to a freely-selected timing designated by the user. However, insuch a case, the following problem occurs.

After the detection image actual measurement in the normal print mode isperformed, the predicted density correction in the wide color gamutprint mode is performed. In some cases, the state of the image formingapparatus 200 exhibited when the predicted density correction in thewide color gamut print mode is performed is different from the state ofthe image forming apparatus 200 exhibited when the detection imageactual measurement in the wide color gamut print mode is performed atthe timing designated by the user. In such a case, the accuracy of thecalculated difference ΔL(i) deteriorates. Originally, the differenceΔL(i) to be calculated indicates an individual difference in the imageforming apparatus 200 including the cartridge. However, when a timing toperform the predicted density correction in the wide color gamut printmode and the timing to perform the detection image actual measurement inthe wide color gamut print mode are different, the difference ΔL(i)involves changes due to, for example, variations ascribable to theprogress of use and environmental variations. In the second embodiment,in consideration of such a problem, the state of the image formingapparatus 200 exhibited at the time of performing the predicted densitycorrection in the wide color gamut print mode and the state of the imageforming apparatus 200 exhibited at the time of performing the detectionimage actual measurement in the wide color gamut print mode are comparedwith each other, and the difference ΔL(i) exhibited when the states arethe closest to each other is employed as the correction value. Thecontroller 201 stores the before-correction γ curve Lγdetected(i)exhibited at the time of performing the detection image actualmeasurement and the difference ΔL(i) in the nonvolatile memory 230, andinformation relating to the image forming apparatus state exhibited whenthe difference ΔL(i) was calculated is also stored in association withthe difference ΔL(i).

Further, in the second embodiment, the timing to perform the detectionimage actual measurement is set to the freely-selected timing designatedby the user. The image forming apparatus 200 includes the operating unit300 serving as a designation unit, and the user designates the timing toperform the detection image actual measurement through the operatingunit 300. The operating unit 300 is, for example, a touch panel liquidcrystal display. In another case, the user may designate the timingthrough a printer driver running on a personal computer or other suchexternal apparatus connected to the image forming apparatus 200.

[Regarding Density Control in Second Embodiment]

A control procedure in the second embodiment is described with referenceto the flow chart illustrated in FIG. 12. The description is followed bythe verification of the effects. When the image forming apparatus 200 isactivated, the controller 201 performs processing of Step S12 and thesubsequent steps. In Step S12, the controller 201 performs the detectionimage actual measurement in the normal print mode. With this processing,the before-correction γ curve Rγdetected(i) in the normal print mode iscalculated while the γ correction at the time of the normal print modeis performed.

In Step S13, the controller 201 calculates the following value from suchcorrelation tables as shown in FIG. 7A, FIG. 7B, and FIG. 8B based onparameters including the circumferential speed difference of thedeveloping roller 303 exhibited when the detection image actualmeasurement is performed, the degree of use of the drum unit 310, andthe degree of toner consumption. That is, the controller 201 calculatesLγpredicted(i) from the before-correction γ curves Rγdetected(i) andΔLpredicted(i) in order to obtain the before-correction γ curve in thewide color gamut print mode based on the predicted density correction.Details of Lγpredicted(i) are as described in the first embodiment.

In Step S14, the controller 201 determines whether the difference ΔL(i)is stored in the nonvolatile memory 230. Details of the difference ΔL(i)are as described in the first embodiment.

When determining in Step S14 that the difference ΔL(i) is not stored inthe nonvolatile memory 230, the controller 201 advances the processingto Step S15. In Step S15, the controller 201 determines whether it isdesignated by the user to perform the detection image actual measurementin the wide color gamut print mode. When determining in Step S15 that itis designated by the user to avoid performing the detection image actualmeasurement in the wide color gamut print mode, the controller 201advances the processing to Step S16. In Step S16, the controller 201recreates a look-up table (performs the γ correction) from thebefore-correction γ curve Lγpredicted(i) in the wide color gamut printmode based on the predicted density correction, which is calculated inStep S13, and performs the image formation in the wide color gamut printmode to bring the processing to an end. In the processing of Step S16,the detection image actual measurement is not performed, and thedifference ΔL(i) is not stored in the nonvolatile memory 230, to therebyavoid performing the correction of the before-correction γ curveLγpredicted(i) based on the difference ΔL(i) as well.

When determining in Step S15 that it is designated by the user toperform the detection image actual measurement in the wide color gamutprint mode, the controller 201 advances the processing to Step S17. InStep S17, the controller 201 performs the detection image actualmeasurement in the wide color gamut print mode to calculate thebefore-correction γ curve Lγdetected(i). The controller 201 stores thecalculated before-correction γ curve Lγdetected(i) and the informationindicating the current state of the image forming apparatus 200 in thenonvolatile memory 230. In Step S18, the controller 201 calculates thedifference ΔL(i) from the before-correction γ curve Lγdetected(i) in thewide color gamut print mode based on the detection image actualmeasurement, which is calculated in Step S17, and the before-correctionγ curve Lγpredicted(i) in the wide color gamut print mode based on thepredicted density correction, which is calculated in Step S13. In thiscase, the difference ΔL(i) is expressed by Lγdetected(i)−Lγpredicted(i).In Step S19, the controller 201 calculates Lγcorrected(i)(=Lγpredicted(i)+ΔL(i)). In Step S20, the controller 201 recreates alook-up table from Lγcorrected(i) calculated in Step S19 (performs the γcorrection), and performs the image formation in the wide color gamutprint mode to bring the processing to an end.

When determining in Step S14 that the difference ΔL(i) is stored in thenonvolatile memory 230, the controller 201 advances the processing toStep S21. In Step S21, the controller 201 determines whether it isdesignated by the user to perform the detection image actual measurementin the wide color gamut print mode. When determining in Step S21 that itis designated by the user to avoid performing the detection image actualmeasurement in the wide color gamut print mode, the controller 201advances the processing to Step S19. In Step S19, the controller 201uses the difference ΔL(i) stored in the nonvolatile memory 230 tocalculate Lγcorrected(i) without performing the detection image actualmeasurement. The subsequent processing steps have been described above,and descriptions thereof are omitted.

When determining in Step S21 that it is designated by the user toperform the detection image actual measurement in the wide color gamutprint mode, the controller 201 advances the processing to Step S22. InStep S22, the controller 201 performs the detection image actualmeasurement in the wide color gamut print mode to calculate thebefore-correction γ curve Lγdetected(i). The controller 201 stores thecalculated before-correction γ curve Lγdetected(i) and the informationindicating the current state of the image forming apparatus 200 in thenonvolatile memory 230.

In Step S23, the controller 201 performs the following processing inorder to determine whether the difference ΔL(i) is required to beupdated. That is, it is determined which image forming apparatus stateis the closest to the image forming apparatus state exhibited when thecurrent Lγpredicted(i) was obtained from among the image formingapparatus states exhibited when the detection image actual measurementin the wide color gamut print mode was performed in the past and theimage forming apparatus state exhibited in Step S22, which are stored inthe nonvolatile memory 230. Specifically, the controller 201successively compares the current image forming apparatus state with aplurality of image forming apparatus states in the past and the imageforming apparatus state exhibited in Step S22, which are stored in thenonvolatile memory 230, and identifies Lγdetected(i) associated with theimage forming apparatus state closest to the image forming apparatusstate exhibited in Step S22 from among those image forming apparatusstates.

As described above, in order to obtain the difference ΔL(i) exhibitinghigh accuracy, it is originally required to perform the detection imageactual measurement along with the predicted density correction. However,in order to place a higher priority on short downtime, when theabove-mentioned control cannot be performed together, the differenceΔL(i) (=Lγdetected(i)−Lγpredicted(i)) is calculated under the conditionthat the states of the image forming apparatus 200 are closer to eachother as much as possible. Therefore, in the second embodiment, theaccuracy of the difference ΔL(i) can be improved.

(Regarding Information Indicating Image Forming Apparatus State)

In the second embodiment, the following three indicators are defined soas to indicate the state of the image forming apparatus 200. Then, a“distance index” is calculated as an index indicating how close thestates of the image forming apparatus 200 exhibited when the predicteddensity correction and the detection image actual measurement areperformed are to each other. It is determined how close the states ofthe image forming apparatus 200 are to each other based on factors thatchange over time.

A. (difference in number of printed sheets)÷(number of printed sheets(for example, 5,000 sheets in the second embodiment) that cause theoutput density to vary by 0.1).

B. (difference in absolute moisture content under the installationenvironment of the image forming apparatus)÷(change in absolute moisturecontent (for example, 2.5 g/m3 in the second embodiment) that causes theoutput density to vary by 0.1)

C. (difference in photosensitive drum temperature)÷(change inphotosensitive drum temperature (for example, 5° C. in the secondembodiment) that causes the output density to vary by 0.1)

In this case, the indicator A indicates a change in density due to thedeterioration of the image forming apparatus 200 caused by performingprinting on the recording materials 203. The indicator B indicates achange in density due to variations in installation environment of theimage forming apparatus 200. The indicator C indicates a change indensity due to a change in photosensitive drum potential (surfacepotential of the photosensitive drum) caused when the resistance of thephotosensitive drum 301 is changed due to a change in temperature of thephotosensitive drum 301. Each of those indicators is normalized bydividing the difference by the condition that causes the output densityto vary by 0.1. The before-correction γ curve Lγdetected(i) involvingthe smallest total value of those indicators A to C is used to calculatethe difference ΔL(i), to thereby be able to improve the accuracy incalculating the difference ΔL(i).

Referring back to the description of the flow chart of FIG. 12, in StepS24, the controller 201 determines whether the before-correction γ curveLγdetected(i) selected (extracted) in Step S23 is the before-correctionγ curve Lγdetected(i) calculated this time by performing the detectionimage actual measurement in Step S22. When determining in Step S24 thatLγdetected(i) selected in Step S23 is not Lγdetected(i) calculated thistime, the controller 201 advances the processing to Step S25. In StepS25, the controller 201 recreates a look-up table for correcting the γcurve into a target γ curve (performs the γ correction) from thebefore-correction γ curve Lγdetected(i) calculated based on thedetection image actual measurement in Step S22. The image formingapparatus then uses the look-up table to perform the image formation inthe wide color gamut print mode to bring the processing to an end. Inthis manner, when the detection image actual measurement is performed inthe wide color gamut print mode before the image formation is performedin the wide color gamut print mode, the before-correction γ curveLγdetected(i) obtained based on the actual measurement is used, tothereby be able to perform the image formation with high accuracy.

When determining in Step S24 that Lγdetected(i) selected in Step S23 isthe before-correction γ curve Lγdetected(i) calculated this time byperforming the detection image actual measurement in Step S22, thecontroller 201 advances the processing to Step S18. In Step S18, thecontroller 201 calculates the difference ΔL(i) from thebefore-correction γ curve Lγdetected(i) based on the detection imageactual measurement, which is calculated in Step S22, and thebefore-correction γ curve Lγpredicted(i) based on the predicted densitycorrection, which is calculated in Step S13. In other words, thecontroller 201 updates the difference ΔL(i). The controller 201 storesthe updated difference ΔL(i) in the nonvolatile memory 230. In Step S19,the controller 201 uses the difference ΔL(i) calculated in Step S18 tocalculate Lγcorrected(i). In Step S20, the controller 201 recreates alook-up table (performs the γ correction) from Lγcorrected(i) calculatedin Step S19, and performs the image formation in the wide color gamutprint mode to bring the processing to an end.

The controller 201 may be configured to monitor whether the detectionimage actual measurement in the normal print mode is to be performed inparallel with the processing from Step S17 to Step S25. When determiningthat the detection image actual measurement in the normal print mode isto be performed during the processing from Step S17 to Step S25, thecontroller 201 may perform the processing of Step S2 and the subsequentsteps in FIG. 10. In this case, when determining that the density hasbeen greatly changed, the controller 201 determines that the detectionimage actual measurement in the normal print mode is to be performed.The case in which the density has been greatly changed corresponds to,for example, a case in which the number of sheets on which an image hasbeen formed has exceeded a predetermined number of sheets since thedetection image actual measurement in the normal print mode wasperformed last or case in which environmental variations have occurred.

[Verification of Effects]

Verification as to how much difference occurs in the accuracy of densitycontrol was performed between the above-mentioned case in which thedensity control is performed by employing the control in the secondembodiment and a case in which the density control is performed by onlythe predicted density correction. For this verification, a method ofperforming examination in the following order while varying theinstallation environment of the image forming apparatus was employed.

[1] Under the environment of a temperature of 23° C. and a humidity of50% (with the absolute moisture content being 8.9 g/m3), the detectionimage actual measurement in the normal print mode is performed to obtainthe before-correction γ curve Lγpredicted(i) based on the predicteddensity correction in the wide color gamut print mode. In addition, thedetection image actual measurement in the wide color gamut print mode isperformed together to obtain the before-correction γ curveLγdetected(i).

[2] In order to cause a change in color impression of the image formingapparatus 200, the installation environment is changed to an environmentof a temperature of 23° C. and a humidity of 55% (with the absolutemoisture content being 9.8 g/m3). As the above-mentioned “distanceindex”, the indicator B is employed, and (9.8−8.9)/2.5=0.36 is obtained.

[3] The detection image actual measurement in the wide color gamut printmode is performed to obtain a before-correction γ curveLγdetected(1)(i). In this case, the before-correction γ curve obtainedafter the installation environment is changed is expressed asLγdetected(1)(i) in distinction from the before-correction γ curveLγdetected(i) of the item [1].

[4] A difference ΔL1(i) is obtained from the before-correction γ curveLγpredicted(i) in the wide color gamut print mode based on the predicteddensity correction ([1]) and the before-correction γ curveLγdetected(1)(i) in the wide color gamut print mode based on thedetection image A ([3]). In this case, the difference is expressed asΔL1(i) in order to clarify that the difference is obtained based on thebefore-correction γ curve Lγdetected(1)(i) obtained in the item [3].

[5] In order to cause a change in color impression of the image formingapparatus 200, the installation environment is changed to an environmentof a temperature of 24° C. and a humidity of 60% (with the absolutemoisture content being 11.3 g/m3). As the “distance index”, theindicator B is employed, and (11.3-8.9)/2.5=0.96 is obtained. That is,the distance index (=0.96) becomes larger this time than the distanceindex (=0.36) of the item [2].

[6] The detection image actual measurement in the wide color gamut printmode is performed to obtain a before-correction γ curveLγdetected(2)(i). In this case, the before-correction γ curve obtainedafter the installation environment is further changed is expressed asLγdetected(2)(i) in distinction from the before-correction γ curveLγdetected(i) of the item [1] and the before-correction γ curveLγdetected(1)(i) of the item [3].

[7] A difference ΔL2(i) is obtained from the before-correction γ curveLγpredicted(i) in the wide color gamut print mode based on the predicteddensity correction ([1]) and the before-correction γ curveLγdetected(2)(i) in the wide color gamut print mode based on thedetection image actual measurement ([6]). In this case, the differenceis expressed as ΔL2(i) in order to clarify that the difference isobtained based on the before-correction γ curve Lγdetected(2)(i)obtained in the item [6].

[8] The before-correction γ curve Lγpredicted(i) in the wide color gamutprint mode based on the predicted density correction, which is obtainedin the item [1], is corrected based on the difference ΔL1(i) obtained inthe item [4] to obtain Lγcorrected(1)(i) (=Lγpredicted(i)+ΔL1(i)). Thebefore-correction γ curve Lγpredicted(i) in the wide color gamut printmode based on the predicted density correction, which is obtained in theitem [1], is also corrected based on the difference ΔL2(i) obtained inthe item [7] to obtain Lγcorrected(2)(i) (=Lγpredicted(i)+ΔL2(i)). It isthen examined which one of Lγcorrected(1)(i) and Lγcorrected(2)(i) iscloser to the before-correction γ curve Lγdetected(i) in the wide colorgamut print mode based on the detection image actual measurement, whichis obtained in the item [1].

FIG. 13 is a graph for showing the before-correction γ curveLγpredicted(i) in the wide color gamut print mode based on the predicteddensity correction and the before-correction γ curve Lγdetected(i) inthe wide color gamut print mode based on the detection image actualmeasurement, which are obtained by the above-mentioned verification. InFIG. 13, Lγcorrected(1)(i) (=Lγpredicted(i)+ΔL1(i)) andLγcorrected(2)(i) (=Lγpredicted(i)+ΔL2(i)) are also shown. In FIG. 13,the horizontal axis represents the input image data, and the verticalaxis represents the output density on the recording material 203. Thecurved line indicated by the broken line and the sign “×” indicates thebefore-correction γ curve Lγpredicted(i) in the wide color gamut printmode based on the predicted density correction. The curved lineindicated by the solid line and the sign “∘” indicates thebefore-correction γ curve Lγdetected(i) in the wide color gamut printmode based on the detection image actual measurement. The curved lineindicated by the dotted line and the solid sign “A” indicatesLγcorrected(1)(i) (=Lγpredicted(i)+ΔL1(i)). The curved line indicated bythe broken line and the sign “⋄” indicates Lγcorrected(2)(i)(=Lγpredicted(i)+ΔL2(i)). In FIG. 13, the low density side (0h to 80h ofthe input image data), which exhibits a large density difference, isenlarged for the sake of easy viewing.

As shown in FIG. 13, the result indicates that Lγcorrected(1)(i)(=Lγpredicted(i)+ΔL1(i)) relating to a small distance index is closer tothe before-correction γ curve Lγdetected(i) of the item [1] thanLγcorrected(2)(i) (=Lγpredicted(i)+ΔL2(i)) relating to a large distanceindex. It was successfully verified from the above-mentioned resultthat, when the control in the second embodiment is employed, a stablecolor impression can be reproduced while the frequency of performing thedetection image actual measurement is reduced even in a case whereneither the predicted density correction nor the actual measurementdensity control can be performed.

There are no particular limitations imposed on the indicator indicatingthe state of the image forming apparatus 200 described in the secondembodiment, and an optimum configuration may be employed in accordancewith the image forming apparatus to be used. Further, in the secondembodiment, the difference ΔL(i) is again calculated when the detectionimage actual measurement in the wide color gamut print mode isperformed, but may be again calculated when, for example, the predicteddensity correction is performed.

According to the second embodiment described above, the reduction ofdowntime relating to the formation and detection of the detection imagecan be further achieved in response to demand from users.

Third Embodiment

A third embodiment of the present disclosure relates to the same controlas that in the first embodiment except for the following point. That is,the γ curve is used to calculate the difference ΔL(i) in the firstembodiment and the second embodiment, while the LUT (look-up table) isused for the calculation in the third embodiment.

[Outline of Configuration of Image Forming Apparatus]

Basic configurations and operations of the image forming apparatus, thedetection image actual measurement, and the predicted density correctionthat are to be used in the third embodiment are the same as thosedescribed in the first embodiment. Therefore, duplicate detaileddescriptions in the third embodiment are omitted.

[Regarding Density Control in Third Embodiment]

Now, a method of calculating a difference between the predicted densitycorrection and the detection image actual measurement in the thirdembodiment through use of a look-up table (LUT) different from that inthe first embodiment to correct the predicted density correctioninformation is described with reference to the flowchart illustrated inFIG. 14. When the image forming apparatus 200 is activated, thecontroller 201 starts processing of Step S31 and the subsequent steps.In Step S31, the controller 201 performs the detection image actualmeasurement in the normal print mode to perform the γ correction at thetime of the normal print mode, and obtains a look-up tableR_(LUT)detected(i) in the normal print mode. This look-up tableR_(LUT)detected(i) corresponds to a first conversion unit.

In Step S32, the controller 201 obtains a correction valueΔL_(LUT)predicted of the look-up table R_(LUT)detected(i) in thefollowing manner. That is, the controller 201 obtains a correction valueΔL_(LUT)predicted(i) in the case of effecting the wide color gamut printmode from such correlation tables as shown in FIG. 7A, FIG. 7B, and FIG.8B based on parameters including the circumferential speed difference ofthe developing roller 303 exhibited when the detection image actualmeasurement is performed, the degree of use of the drum unit 310, andthe degree of toner consumption. A before-correction look-up tableL_(LUT)predicted(i) based on the predicted density correction in thewide color gamut print mode is expressed by the following expression.

L _(LUT)predicted(i)=R _(LUT)detected(i)+ΔL_(LUT)predicted(i)  Expression (4)

In Step S33, the controller 201 determines whether a difference ΔL_(LUT)(i) is stored in the nonvolatile memory 230 mounted to the image formingapparatus 200. In this case, the difference ΔL_(LUT) (i) refers to adifference (L_(LUT)detected(i)−L_(LUT)predicted(i)) between abefore-correction look-up table L_(LUT)detected(i) based on thedetection image actual measurement in the wide color gamut print modeand the before-correction look-up table L_(LUT)predicted(i) based on thepredicted density correction in the wide color gamut print mode. In thiscase, the before-correction look-up table L_(LUT)detected(i) correspondsto a conversion unit. In addition, the difference ΔL_(LUT)(i)corresponds to correction information.

As described above, it is highly possible that the accuracy of thedetection image actual measurement using the density sensor 218 issuperior to that of the predicted density correction in which it isdifficult to correct individual differences. When the before-correctionlook-up table L_(LUT)detected(i) in the wide color gamut print modebased on the detection image actual measurement is present, thedifference is used to correct the before-correction look-up tableL_(LUT)predicted(i) based on the predicted density correction in thewide color gamut print mode. With this configuration, it is possible tocorrect the individual difference of the image forming apparatus 200.The expression of the difference ΔL_(LUT)(i) is expressed by Expression(5).

ΔL _(LUT)(i)=L _(LUT)detected(i)−L _(LUT)predicted(i)  Expression (5)

When determining in Step S33 that the difference ΔL_(LUT)(i) is notstored, the controller 201 advances the processing to Step S34. In StepS34, the controller 201 performs the detection image actual measurementin the wide color gamut print mode. In Step S35, the controller 201 usesExpression (5) to calculate the difference ΔL_(LUT)(i). In Step S36, thecontroller 201 corrects the before-correction look-up tableL_(LUT)predicted(i) based on the predicted density correction in thewide color gamut print mode. The corrected look-up table is set asL_(LUT)corrected(i). The correction expression to be used is Expression(6).

L _(LUT)corrected(i)=L _(LUT)predicted(i)+ΔL _(LUT)(i)  Expression (6)

The predicted density correction and the detection image actualmeasurement in the wide color gamut print mode are performedsimultaneously. Therefore, L_(LUT)corrected(i)=L_(LUT)detected(i) isestablished immediately after the detection image actual measurement isperformed. After that, the predicted density correction is performed, tothereby update L_(LUT)predicted(i) and update L_(LUT)corrected(i) aswell.

When determining in Step S33 that ΔL_(LUT)(i) is stored after thedetection image actual measurement in the wide color gamut print modewas performed in the past, the controller 201 advances the processing toStep S36. In Step S37, the controller 201 uses L_(LUT)corrected(i)calculated by Expression (6) in Step S36 to perform the image formationwhen the user performs the wide color gamut print mode. In Step S38, thecontroller 201 determines whether the condition for performing thedetection image actual measurement in the normal print mode has beensatisfied. When determining in Step S38 that the condition forperforming the detection image actual measurement has been satisfied,the controller 201 returns the processing to Step S31. When determiningin Step S38 that the condition for performing the detection image actualmeasurement has not been satisfied, the controller 201 returns theprocessing to Step S37, and uses the look-up table obtained in Step S37to perform the image formation until the detection image actualmeasurement is performed. The detection image actual measurement isperformed when it is feared that the image forming apparatus 200 mayhave the color impression changed due to sheet-passing endurance, thereplacement of the cartridge, or a change in use environment, and when aperforming condition for the detection image actual measurement in thenormal print mode is satisfied, the controller 201 advances to theprocessing of Step S31 again.

There are no particular limitations imposed on the configurations of thedetection image actual measurement and the predicted density correctiondescribed in the third embodiment, and an optimum configuration may beemployed in accordance with the image forming apparatus to be used. Inthe third embodiment, when the difference ΔL_(LUT)(i) is not stored, thedetection image actual measurement in the wide color gamut print mode isperformed to calculate ΔL_(LUT)(i). However, even when the differenceΔL_(LUT)(i) is stored, density correction may be performed as required,to thereby calculate the difference ΔL_(LUT)(i) again.

According to the third embodiment described above, the reduction ofdowntime relating to the formation and detection of the detection imagecan be further achieved in response to demand from users.

Other Embodiment

In the first embodiment and the second embodiment, Lγpredicted(i) in thewide color gamut print mode is obtained from Rγdetected(i) in the normalprint mode, and Lγdetected(i) is further obtained to obtain thedifference ΔL(i). When, for example, the difference ΔL(i) is stored inthe nonvolatile memory 230, the difference ΔL(i) is used to correctLγpredicted(i) and obtain Lγcorrected(i). However, Lγcorrected(i) may beobtained based on a difference between Lγdetected(i) in the wide colorgamut print mode and Rγdetected(i) in the normal print mode. In thiscase, Lγcorrected(i) is obtained by, for example, the followingexpression.

Lγcorrected(i)=Rγdetected(i)+(Lγdetected(i)−Rγdetected(i))

In order to calculate the difference, the value obtained under the samecondition or as close a condition as possible is used to increase theaccuracy. Therefore, it is to be understood that the accuracy is higherwhen the difference ΔL(i) is used than when the difference(Lγdetected(i)−Rγdetected(i)) is used.

The same applies to a method of using the look-up table in the thirdembodiment.

According to the other embodiment described above, the reduction ofdowntime relating to the formation and detection of the detection imagecan be further achieved in response to demand from users.

Although the exemplary embodiments of the present disclosure have beendescribed so far, the present disclosure is by no means limited to thoseembodiments, and hence various changes and modifications can be madewithin the scope of the subject matter of the present disclosure.

Further, the present disclosure is also achieved by performingprocessing for supplying software (a program) for implementing theabove-mentioned functions in the embodiments to a system or an apparatusthrough a network or each of different kinds of storage media andcausing a computer (or, for example, a CPU or an MPU) of the system orthe apparatus to read and perform the program.

According to the present disclosure, it is possible to reduce downtimerelating to the formation and detection of the detection image.

While the present disclosure has been described with reference toexemplary embodiments, it is to be understood that the disclosure is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2017-223072, filed Nov. 20, 2017, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image forming apparatus, comprising: aphotosensitive drum; a developing roller configured to develop anelectrostatic latent image on the photosensitive drum with a toner toform a toner image; a belt onto which the toner image formed on thephotosensitive drum is to be transferred or on which a recordingmaterial, onto which the toner image is to be transferred, is borne; adetector configured to detect a density of a detection image formed onthe belt, wherein the image forming apparatus is configured to performan image formation in a first mode in which a circumferential speeddifference of a circumferential speed of the developing roller withrespect to a circumferential speed of the photosensitive drum is a firstcircumferential speed difference and in a second mode in which thecircumferential speed difference is larger than the firstcircumferential speed difference; a controller configured to calculate afirst conversion unit configured to convert a gradation of an inputimage data so that a density output for the input image data becomes afirst density output characteristic based on a first detection result ofthe detection image detected by the detector in the first mode; and astorage, wherein the controller is configured to generate a secondconversion unit configured to convert the gradation of the input imagedata so that the density output for the input image data becomes asecond density output characteristic in the second mode based on thedetection result in the first mode and correction information, andwherein the controller is configured to further update the correctioninformation based on a second detection result of the detection imagedetected by the detector in the second mode and the first detectionresult.
 2. An image forming apparatus according to claim 1, wherein thecontroller is configured to update the correction information based on adifference between the first detection result and the second detectionresult.
 3. An image forming apparatus according to claim 1, wherein thecontroller is configured to generate the second conversion unit based onthe correction information and the first conversion unit obtained basedon the first detection result.
 4. An image forming apparatus accordingto claim 1, wherein the controller is configured to update thecorrection information based on the first conversion unit obtained basedon the first detection result and a conversion unit obtained based onthe second detection result.
 5. An image forming apparatus, comprising:a photosensitive drum; a developing roller configured to develop anelectrostatic latent image on the photosensitive drum with a toner toform a toner image; a belt onto which the toner image formed on thephotosensitive drum is to be transferred or on which a recordingmaterial, onto which the toner image is to be transferred, is borne; adetector configured to detect a density of a detection image formed onthe belt; a controller configured to perform a first detection imageactual measurement for obtaining a first characteristic indicating arelationship between an input image data in a first mode and a densitycorresponding to the input image data based on a result of detecting thedensity of the detection image by the detector in the first mode; and astorage, wherein the controller is configured to perform a predicteddensity correction for predicting, based on the first characteristic, acharacteristic indicating a relationship between an input image data ina second mode in which an image formation is performed with a colorgamut different from a color gamut in the first mode and the densitycorresponding to the input image data, and perform an image formation inthe second mode by using a predicted characteristic, wherein thecontroller is configured to perform a second detection image actualmeasurement for obtaining a second characteristic indicating arelationship between the input image data in the second mode and thedensity corresponding to the input image data based on a result ofdetecting the density of the detection image by the detector in thesecond mode, obtain a correction value based on the secondcharacteristic and the predicted characteristic, and correct thepredicted characteristic by using an obtained correction value whilestoring the obtained correction value in the storage, and wherein thecontroller is configured to further correct the predicted characteristicby using the obtained correction value stored in the storage withoutperforming the second detection image actual measurement.
 6. An imageforming apparatus according to claim 5, wherein the correction valuecomprises a difference between the second characteristic and thepredicted characteristic.
 7. An image forming apparatus according toclaim 5, further comprising a designation unit configured to designatewhether the second detection image actual measurement is to beperformed, wherein in a case in which it is designated by thedesignation unit to perform the second detection image actualmeasurement, the controller is configured to perform the seconddetection image actual measurement irrespective of whether the obtainedcorrection value is stored in the storage.
 8. An image forming apparatusaccording to claim 7, wherein in a case in which the obtained correctionvalue is not stored in the storage and it is designated by thedesignation unit not to perform the second detection image actualmeasurement, the controller is configured to use the predictedcharacteristic for the image formation in the second mode withoutcorrecting the predicted characteristic.
 9. An image forming apparatusaccording to claim 7, wherein in a case in which the obtained correctionvalue is not stored in the storage and it is designated by thedesignation unit to perform the second detection image actualmeasurement, the controller is configured to perform the seconddetection image actual measurement to obtain the second characteristic,calculate the correction value based on an obtained secondcharacteristic, correct the predicted characteristic based on acalculated correction value, and use a corrected predictedcharacteristic for the image formation in the second mode.
 10. An imageforming apparatus according to claim 7, wherein the storage stores afirst image forming apparatus state exhibited when the second detectionimage actual measurement is performed and a second image formingapparatus state exhibited before the correction value is obtained,wherein the controller is configured to identify, from among a pluralityof second characteristics stored in the storage, an image formingapparatus state closest to an image forming apparatus state exhibitedwhen the predicted characteristic is obtained, and wherein in a case inwhich the image forming apparatus state identified as closest is thefirst image forming apparatus state, the controller is configured toupdate the correction value based on the second characteristic, correctthe predicted characteristic based on an updated correction value, anduse a corrected predicted characteristic for the image formation in thesecond mode.
 11. An image forming apparatus according to claim 10,wherein the controller is configured to identify the image formingapparatus state closest to the image forming apparatus state exhibitedwhen the predicted characteristic is obtained, by an index determinedbased on a factor that changes with a passage of time.
 12. An imageforming apparatus according to claim 11, wherein the factor includes atleast one of a number of sheets on which images have been formed, anabsolute moisture content in an environment in which the image formingapparatus is installed, and a change in temperature of thephotosensitive drum.
 13. An image forming apparatus according to claim7, wherein in a case in which the obtained correction value is stored inthe storage and it is designated by the designation unit not to performthe second detection image actual measurement, the controller isconfigured to correct the predicted characteristic based on the obtainedcorrection value stored in the storage, and use a corrected predictedcharacteristic for the image formation in the second mode.
 14. An imageforming apparatus according to claim 5, wherein the controller isconfigured to obtain the predicted characteristic by the predicteddensity correction based on a result of detecting the detection image bythe detector in the first mode and a parameter for controlling a supplyamount of the toner to be supplied from the developing roller to thephotosensitive drum.
 15. An image forming apparatus according to claim14, wherein the parameter comprises a rotation time of the developingroller or a circumferential speed difference which is a differencebetween a rotation speed of the developing roller with respect to arotation speed of the photosensitive drum.
 16. An image formingapparatus according to claim 15, wherein the controller is configured toobtain an image data for a current photosensitive drum and a currentdeveloping roller and a density ratio between a density obtained in thefirst mode and a density obtained in the second mode based on a data onthe density obtained in each of the first mode and the second mode undera predetermined condition, a current use amount of toner, and a degreeof use of the current photosensitive drum, and to obtain the predictedcharacteristic based on a detection result detected by the detector inthe first mode and the density ratio.
 17. An image forming apparatusaccording to claim 16, wherein the data on the density obtained in eachof the first mode and the second mode under the predetermined conditionincludes: a first density ratio between a density in the first mode anda density in the second mode that have been obtained by use of a newphotosensitive drum and a new developing roller; a second density ratiobetween a density in the first mode and a density in the second modethat have been obtained by use of the new photosensitive drum and adeveloping roller subjected to the image formation on a predeterminednumber of recording materials; a third density ratio between a densityin the first mode and a density in the second mode that have beenobtained by use of a photosensitive drum exhibiting a large degree ofuse and the new developing roller; and a fourth density ratio between adensity in the first mode and a density in the second mode that havebeen obtained by use of the photosensitive drum exhibiting the largedegree of use and the developing roller subjected to the image formationon the predetermined number of recording materials.
 18. An image formingapparatus according to claim 16, further comprising a cartridgeincluding the photosensitive drum, the developing roller, and anonvolatile memory, wherein the nonvolatile memory is configured tostore a data on the current use amount of the toner and a data on thedegree of use of the current photosensitive drum.
 19. An image formingapparatus according to claim 15, wherein the density becomes higher asthe circumferential speed difference becomes larger.
 20. An imageforming apparatus according to claim 15, wherein the density becomeslower as a degree of use of the photosensitive drum becomes larger. 21.An image forming apparatus according to claim 15, wherein the densitybecomes higher as a degree of use of the developing roller becomeslarger until the degree of use of the developing roller reaches apredetermined use amount, and the density maintains a constant levelafter the degree of use of the developing roller reaches thepredetermined use amount.
 22. An image forming apparatus according toclaim 1, wherein the second mode comprises a mode for causing a rotationspeed of the developing roller to become higher than a rotation speed ofthe developing roller in the first mode.
 23. An image forming apparatusaccording to claim 5, wherein the second mode comprises a mode forcausing a rotation speed of the developing roller to become higher thana rotation speed of the developing roller in the first mode.
 24. Animage forming method to be performed by an image forming apparatus, theimage forming apparatus comprising a photosensitive drum, a developingroller configured to develop an electrostatic latent image on thephotosensitive drum with a toner to form a toner image, a belt ontowhich the toner image formed on the photosensitive drum is to betransferred or on which a recording material, onto which the toner imageis to be transferred, is borne, a detector configured to detect adensity of a detection image formed on the belt, wherein the imageforming apparatus is configured to perform an image formation in a firstmode in which a circumferential speed difference of a circumferentialspeed of the developing roller with respect to a circumferential speedof the photosensitive drum is a first circumferential speed differenceand in a second mode in which the circumferential speed difference islarger than the first circumferential speed difference, a controllerconfigured to calculate a first conversion unit configured to convert agradation of an input image data so that a density output for the inputimage data becomes a first density output characteristic based on afirst detection result of the detection image detected by the detectorin the first mode, and a storage, the image forming method comprising:generating, by the controller, a second conversion unit configured toconvert the gradation of the input image data so that the density outputfor the input image data becomes a second density output characteristicin the second mode based on the detection result in the first mode andcorrection information; and further updating, by the controller, thecorrection information based on a second detection result of thedetection image detected by the detector in the second mode and thefirst detection result.
 25. An image forming method to be performed byan image forming apparatus, the image forming apparatus comprising aphotosensitive drum, a developing roller configured to develop anelectrostatic latent image on the photosensitive drum with a toner toform a toner image, a belt onto which the toner image formed on thephotosensitive drum is to be transferred or on which a recordingmaterial, onto which the toner image is to be transferred, is borne, adetector configured to detect a density of a detection image formed onthe belt, a controller configured to perform a first detection imageactual measurement for obtaining a first characteristic indicating arelationship between an input image data in a first mode and a densitycorresponding to the input image data based on a result of detecting thedensity of the detection image by the detector in the first mode, and astorage, the image forming method comprising: performing, by thecontroller, a predicted density correction for predicting, based on thefirst characteristic, a characteristic indicating a relationship betweenan input image data in a second mode in which an image formation isperformed with a color gamut different from a color gamut in the firstmode and the density corresponding to the input image data, andperforming an image formation in the second mode by using a predictedcharacteristic; performing, by the controller, a second detection imageactual measurement for obtaining a second characteristic indicating arelationship between the input image data in the second mode and thedensity corresponding to the input image data based on a result ofdetecting the density of the detection image by the detector in thesecond mode, obtaining a correction value based on the secondcharacteristic and the predicted characteristic, correcting thepredicted characteristic by using an obtained correction value whilestoring the obtained correction value in the storage; and furthercorrecting, by the controller, the predicted characteristic by using theobtained correction value stored in the storage without performing thesecond detection image actual measurement.